Gas turbine engines such as those used on jet aircraft generally comprise an air inlet, a single or multi-stage compressor, a combustion chamber aft of the compressor, a turbine and an exhaust nozzle. Air entering the inlet flows through the compressor and into the combustion chamber where it provides oxygen for fuel combustion. The hot combustion gases pass through the turbine and exit the exhaust nozzle, providing thrust.
Modern gas turbine engines employ very high working temperatures in order to increase engine operating efficiency. These high temperatures pose a risk of damage to engine components such as turbine blades and vanes. High melting point super-alloys and thermal barrier coatings have been used to avoid thermally induced damage, but operating temperatures can still exceed super-alloy melting points, and coatings can become damaged or otherwise fail over time.
Cooling fluids also may be used to protect engine components exposed to high temperature. One method of using cooling fluids is impingement cooling, which involves directing a relatively cool fluid, such as compressor bleed air, against a surface of a component exposed to high temperatures in order to absorb thermal energy into the cooling fluid which is then carried away from the component. Another method of using cooling fluids is film cooling. Film cooling involves providing a flow of relatively cool fluid from film cooling holes in order to create a thermally insulative barrier between a surface of a component and a relatively hot fluid flow.
For example, turbine blades may be equipped with cooling holes along the turbine blade perimeter. Cooling air from, say, a compressor bleed system, may be ejected through the cooling holes to provide a thermally insulative barrier along a portion of the blade.
A difficulty exists in maintaining a steady film of cooling air across the surface to be cooled. For example, cooling holes can create a vortex of cooling air that draws the hot air against the surface to be cooled instead of away from the surface.
Thus there is a need for an improved film cooling system that provides a steady film of cooling air across the surface to be cooled.